Hydraulic driving system

ABSTRACT

There is provided a hydraulic driving system having two independent driving cycles and comprising two double-acting piston-cylinder assemblies, each of the pistons of which have a specific starting position and is arranged to move from said position through the medium of an interlocking means only when the other piston occupies its starting position.

United States atent 1 Leijon [111 3,744,373 1 July 10, 1973 HYDRAULICDRIVING SYSTEM [76] Inventor: Tage Nils Wilhelm Leijon,

Sturevagen 18, S-182 74 Stocksund, Sweden [22] Filed: Oct. 12, 1971 [21]Appl. N0.: 188,007

[30] Foreign Application Priority Data Feb. 10, 1971 Sweden 1680/71 [52]US. Cl 91/178, 91/189, 91/447 [51] Int. Cl. F0ll 15/00, F011 33/00 [58]Field of Search 91/191, 178, 189,

[56] References Cited UNITED STATES PATENTS 2,264,518 12/1941 Foster..91/191 12/1958 Monteiius 91/191 2/1960 Sharpe eta] ..91/191 PrimaryExaminer-Paul E. Maslousky Att0rne v Ralph E. Parker, Eugene J. Robertset al.

[5 7 ABSTRACT There is provided a hydraulic driving system having twoindependent driving cycles and comprising two double-actingpiston-cylinder assemblies, each of the pistons of which have a specificstarting position and is arranged to move from said position through themedium of an interlocking means only when the other piston occupies itsstarting position.

4 Claims, 2 Drawing Figures HYDRAULIC DRIVING SYSTEM The presentinvention relates to a hydraulic driving system having two drivingcycles which are independent of each other, the system comprising twodoubleacting piston-cylinder assemblies, each of the pistons of whichhave a specific starting position. The system according to the presentinvention is mainly characterized by an interlocking device soconstructed that the piston of one of the piston-cylinder assemblies ismovable from its starting position only when the piston of the otherpiston-cylinder assembly occupies its starting position.

A hydraulic driving system constructed in accordance with the inventioncan be used as a driving means for machines, apparatus etc. which carryout two separate, cyclic operations, of which one cycle may start onlywhen the device associated with the second cycle has reached itsstarting position. For example, the system is suitable for use withside-tipping loader buckets or excavator scoops of the type which tiptowards both sides. When applied to such buckets the system of thepresent invention can be used in a number of different ways. Forexample, it can either be used solely for laterally tipping the bucketsor solely to operate the locking means which retain the buckets inposition during the different tipping movements, and can also be used toprovide both the actual tipping movements and for operating the bucketposition locking means.

The system of the present invention affords considerable advantages overknown, multi-purpose hydraulic driving systems. For example, the systemof the present invention is much more compact than the driving systemdescribed in my Swedish Pat. No. 317 030, this system comprising onepiston-cylinder assembly having a common piston rod which projects outfrom both sides of the assembly, and despite its compactness is morerobust than the known system and has short and strong piston rods,thereby reducing to some extent its volume, which in turn enables it tobe installed within a smaller space than the known system, a featurewhich is highly significant with respect, for example, to loader bucketsand excavator scoops, with which a robust driving system which requiresbut a small installation space is always desirable.

The 11.8. Pat. No. 3 419 l7l describes a hydraulic driving system forlateral and front tipping loaders. This known system is provided withtwo single-acting cylinders provided with spring loaded pistons. Thedisadvantage with this system is that too much force is required toovercome the inherent strength of the springs and that the system isbulky and requires a relatively large installation space. Thesedisadvantages are eliminated with the system of the present invention,which also locks one piston while the other works, a feature which isnot found in the known system.

The system of the present invention also affords advantages of theaforementioned type when compared with the hydraulic driving systemknown from the French Pat. No. l 366 024, in which are installedspring-loaded pistons, and thus no double-acting piston-cylinderassemblies, and with which system the movements of the two pistons canonly be locked in a manner such that one piston is unable to move whilethe other is moving and thus the pistons are not capable of being lockednormally in their starting positions.

The invention will now be described in more detail with reference to theaccompanying drawing, in which FIG. 1 illustrates diagrammatically anembodiment of the invention, and FIG. 2 shows the embodiment shown inFIG. 1 in a more detailed, practical illustration.

As will be seen from the drawing, a hydraulic driving system accordingto the invention includes two doubleacting piston-cylinder assemblies 1,2 having pistons 3, 4. Each of the pistons has a specific startingposition and each of the pistons is capable of being moved through themedium of an interlocking means 5 in a direction from its startingposition only when the other piston is located in its starting position.

The actual interlocking means 5 comprises at least one hydraulic meansand is controlled both mechanically and hydraulically. The system in itsentirety is capable of being operated solely by three different controlpulses sent from an operating means 6, for example in the form of afour-path hydraulic valve of known design, the control pulses beingtransmitted to the system through two hydraulic connecting lines 7,8.The system is connected to a hydraulic driving circuit, indicated in thedrawing by the reference A, via the operating means 6.

It will be evident from FIG. 2, which illustrates the twopiston-cylinder assemblies 1,2 connected to form a single unit with theinterlocking means therebetween as a common end wall piece, that theinterlocking means 5 need only be provided with one single movingelement, namely a sliding piston 9. The piston 9 is provided on its endsurface facing the piston-cylinder assembly 1, to the left of theFigure, with a pressure surface which is exposed to a chamber 12 locatedbetween the interlocking means 5, which also serves as an end wallpiece, and the piston 3 in the piston-cylinder assembly 1 and whichcommunicates with an annular chamber 13 located in the interlockingmeans 5 through a channel 14 disposed in the sliding piston 9. Thesliding piston 9 is also provided with an annular pressure surface 11which is acted upon in a direction opposite to the pressure surface 10and arranged on a cylindrical collar portion located on the centreportion of the sliding piston, the area of the annular pressure surface11 being greater than the area of the pressure surface 10 facing thepiston-cylinder assembly 1.

The hydraulic line 8 extending from the operating means 6 is connectedto the annular chamber 13 and also communicates, via the channel 14 inthe slide piston 9, with the chamber 12 between the piston 3 of thepiston-cylinder assembly 1 and the interlocking means 5, which alsoserves as an endwall piece. Furthermore, the hydraulic line 8 isconnected with the chamber within the outer end of the piston-cylinderassembly 2, shown to the right of the drawing, through a constantly openline 15.

As will be seen from FIG. 2, the interlocking means 5 is symmetrical,and hence the sliding piston 9 also includes a second channel 16 whichcorresponds to the channel 14 and which extends between a chamber 17located between the other end of the interlocking means 5 and the piston4 of the piston-cylinder assembly 2, and a second annular chamber 18 atthe other end of the cylindrical collar portion of the sliding piston 9.The hydraulic line 7 is connected with the second annular chamber 18 andcommunicates, via the second channel 16 in the sliding piston 9 with thechamber 17 located between the piston 4 of the piston-cylinder assembly2 and the interlocking means 5. The hydraulic line 7 also communicateswith the space within the outer end of the piston-cylinder assembly 1,via a constantly open line 19. Arranged in the space between the piston4 and the interlocking means 5 and in the second annular chamber 18 atthe other end of the cylindrical collar portion of the sliding piston 9are pressure surfaces 20 and 21 respectively, the area of the pressuresurface located in the last mentioned space being greater than thatlocated in the first mentioned space. In short, it can be said that thefour pressure surfaces 10,11,20,21 are arranged in opposed relationshipon the ends of the sliding piston and on the ends of the cylindricalcollar portion located thereon, the areas of the surfaces 10,20 arrangedon the ends of the piston being equal but smaller than the areas ofannular surfaces 1 1,21 located on the ends of the collar portion, thearea of the surfaces 11,21 also being equal but greater than the area ofthe surfaces 10,20 located on the ends of the piston. The pressuresurfaces 11,21 of larger area communicate through their respectivechannels 14,16 in the sliding piston 9 with the opposed pressuresurfaces of smaller area arranged on the opposite end of the slidingpiston. The cylindrical collar on the sliding piston 9 serves as a valvemeans during movement of the piston for controlling the flow of pressuremedium to and from the two annular chambers 13 and 18.

The mode of operation of the illustrated embodiment of the systemaccording to the invention will be evident from the following.

In the drawing, the pistons 3,4 of the two pistoncylinder assemblies 1,2are shown occupying their inner end positions, which comprise thestarting positions for the working cycle of the pistons. The hydraulicpistons 3,4 act mechanically against each end of the sliding piston 9 tomaintain it in a central position. In this position the connection fromone of the hydraulic lines 8 to the chamber 12 at one end of the slidingpiston 9, having the associated pressure surface 10, and to the annularchamber 13 at the oppostie end of the collar and having the pressuresurface 1 1, is open but presents a constricted through-flow area, whilethe connection to the space within the outer end of the pistoncylinderassembly 2 is fully open. At the same time, the connection from thesecond hydraulic line 7 to the two corresponding chambers 17,18 and thepressure surfaces 20,21 located on the opposite ends of the slidingpiston and the collar, respectively, is also open but presents arestricted through-flow area while the connection to the space withinthe outer end of the opposing piston-cylinder assembly 1 is fully open,

Subsequent'to setting the operating means 6, pressure medium is suppliedthrough the hydraulic line 8 at the same time as pressure medium isremoved through the hydraulic line 7, and the piston 4 in thepistoncylinder assembly 2 is actuated by the supplied pressure medium ina manner to hold the piston in its starting position. As a result of theconstricted through-flow area of the fluid inlet at the ends of thecylindrical collar on the sliding piston 9, which collar also acts as avalve means, there is a restricted supply of pressure medium to theannular chamber 13 and from there to the chamber 12 between the piston 3of the piston-cylinder assembly 1 and the inter-locking means 5, via thechannel 14 in the sliding piston 9. This restricted supply of pressuremedium to the chamber 12 causes the piston 3 in the piston-cylinderassembly 1 to move outwardly from its inner end position, the slidingpiston 9 moving in the same direction until it reaches a stop positiondetermined by its cylindrical collar as a result of the fact that thepressure surface 11 arranged on the collar and acted upon by thepressure prevailing in the annular chamber 13 is of greater area thanthe pressure surface 10 arranged on the opposite end of the slidingpiston and actuated by a pressure of equal magnitude prevailing in thechamber 12. As a result of this movement of the sliding piston, theconnection from the hydraulic line 8 to the chamber 12 located betweenthe piston 3 of the piston-cylinder assembly 1 and the interlockingmeans 5 is fully opened, whereby the piston 3 moves at full speed uponcontinued outward movement. At the same time, because of the collar onthe sliding piston 9, the connection between the second hydraulic line 7and the chamber 17 between the piston 4 and pistoncylinder 2 and theinterlocking means 5 is fully closed, thereby ensuring that the piston 4does not make a working stroke.

In order to return the piston 3 of the piston-cylinder assembly 1 to itsstarting position, the supply of pressure medium is switched, by meansof the operating means 6, from the hydraulic line 8 to the hydraulicline 7, whereupon pressure medium is drained through the hydraulic line8 under the action of the supply of pressure medium through theconstantly open connection 19, while pressure medium is fed to thesecond hydraulic line 7 and to the space within the outer end of thepiston-cylinder assembly 1, this supply of pressure medium forcing thepiston 3 in the piston-cylinder assembly 1 towards its starting positionand towards the interlocking means 5. Since the pressure surfaces 10 andl 1 are now subjected to the pressure prevailing in the hydraulic line 8serving to drain the pressure medium, the sliding piston 9 is maintainedin its left stop position as seen in the drawing, i.e., is displaced ina direction towards the still operating left hand piston-cylinder 1.Thus, the connection is closed between the hydraulic line 7, throughwhich the pressure medium is now being supplied, and the piston 4 of theright hand pistoncylinder assembly 2. Thus, the piston-cylinder assembly2 is also inactive during the return stroke of the pistoncylinderassembly 1, since the interlocking means 5 prevents the piston 4 frommoving from its starting position.

Subsequent to the aforedescribed movement of the piston 3, theinterlocking means 5 is re-set to its starting position by moving thesliding piston 9 mechanically from its left hand stopping position, asseen in the drawing, to its centre position, by the piston 3 as saidpiston, during its return stroke, moves through the last part of itstravel towards its original starting position.

When the sliding piston 9 has reached its central position, either thepiston 3 of the piston-cylinder assembly 1 or the piston 4 of thepiston-cylinder assembly 2 can be caused to effect a working stroke, bysupplying pressure medium to either of the hydraulic lines 7,8 by meansof the operating means 6.

it will be evident from the aforegoing, that neither of the two pistons3,4 are able to move from their starting position when the other pistonhas left its starting position. Thus, when one piston-cylinder assembly1,2 is active and its piston 3,4 is in motion, the other pistoncylinderassembly is inoperative and its piston is locked in its startingposition.

In the exemplary embodiment of the system according to the invention, asillustrated in FIG. 2, the throttling effect which the cylindricalcollar of the sliding piston 9 has on the flow of pressure medium hastwo purposes, firstly, the constricted flow of pressure medium causesthe system to operate slowly around the starting positions of thepistons, and secondly it shortens the length of movement required by thesliding piston to close the inactive piston-cylinder assembly 1,2 atthat moment.

The illustrated system is also provided with nonreturn valves 22,23which serve to take up a portion of the return flow of pressure mediumover the sliding piston 9 and to permit that of the pistons 3,4 of thepistoncylinder assemblies 1,2, which is inactive at the moment, to movethrough a slight distance from its starting position and towards theinterlocking means 5 serving as a common end wall piece for thepiston-cylinder assemblies, this movement being insufficient toinfluence locking of the piston.

As will be evident from the aforegoing, each of the pistons 3,4 of thetwo piston-cylinder assemblies is arranged to remain in or to adopt itsstarting position in response to a guide pulse which causes the otherpiston to move from its starting position. Each of the pistons are alsoarranged to remain in their respective starting positions in response toa guide pulse which causes the other piston to move toward its startingposition.

The invention is not restricted to the described and illustratedembodiment but can be modified within the scope of the following claims.

What I claim is:

l. A hydraulic driving system having two independent driving cyclescomprising a first and a second double-acting piston-cylinder assembly,the piston of each assembly having a specific starting position, and aninterlocking valve means between said assemblies for controllingmovement of said pistons so that one piston may be moved from itsstarting position only when the other piston is maintained at itsstarting position, said valve means including a first and a secondhydraulic inlet and a sliding piston controlling said inlets, means forselectively supplying hydraulic pressure to said inlets, said slidingpiston being at a neutral position when the first and second pistons areat their starting positions and being movable from its neutral positionin one direction to a first position when subject to hydraulic pressurethrough the first inlet so as to close the second inlet and to admithydraulic pressure to said first piston to move it from its startingposition, means for simultaneously supplying hydraulic pressure to theouter end of the second piston to maintain it in its starting position,and means for supplying hydraulic pressure to the outer end of the firstpiston when at the outer end of its cylinder when desired to return saidfirst piston to its starting position, said sliding valve remaining inits first position until said first piston has returned to its startingposition and returns said sliding piston to its neutral position, thesame functions occurring in opposed relation when hydraulic pressure issupplied to said second inlet.

2. A hydraulic driving system as claimed in claim 1 wherein said slidingpiston is provided with two sets of opposed pressure surfaces of unequalarea, one set of said surfaces being subject to the hydraulic pressuresupplied through one of said inlets to move the sliding valve from itsneutral position.

3. A hydraulic driving system as claimed in claim 2 wherein said slidingvalve is provided with two channels therethrough, each channel affordingcommunication between the surfaces of unequal area of one set.

4. A hydraulic driving system as claimed in claim 1 wherein thecylinders of said assemblies are disposed co-axially on opposed sides ofsaid interlocking valve means and secured thereto and said pistons, whenin their starting positions, abut said sliding piston when the latter isin its neutral position.

1. A hydraulic driving system having two independent driving cyclescomprising a first and a second double-acting pistoncylinder assembly,the piston of each assembly having a specific starting position, and aninterlocking valve means between said assemblies for controllingmovement of said pistons so that one piston may be moved from itsstarting position only when the other piston is maintained at itsstarting position, said valve means including a first and a secondhydraulic inlet and a sliding piston controlling said inlets, means forselectively supplying hydraulic pressure to said inlets, said slidingpiston being at a neutral position when the first and second pistons areat their starting positions and being movable from its neutral positionin one direction to a first position when subject to hydraulic pressurethrough the first inlet so as to close the second inlet and to admithydraulic pressure to said first piston to move it from its startingposition, means for simultaneously supplying hydraulic pressure to theouter end of the second piston to maintain it in its starting position,and means for supplying hydraulic pressure to the outer end of the firstpiston when at the outer end of its cylinder when desired to return saidfirst piston to its starting position, said sliding valve remaining inits first position until said first piston has returned to its startingposition and returns said sliding piston to its neutral position, thesame functions occurring in opposed relation when hydraulic pressure issupplied to said second inlet.
 2. A hydraulic driving system as claimedin claim 1 wherein said sliding piston is provided with two sets ofopposed pressure surfaces of unequal area, one set of said surfacesbeing subject to the hydraulic pressure supplied through one of saidinlets to move the sliding valve from its neutral position.
 3. Ahydraulic driving system as claimed in claim 2 wherein said slidingvalve is provided with two channels therethrough, each channel affordingcommunication between the surfaces of unequal area of one set.
 4. Ahydraulic driving system as claimed in claim 1 wherein the cylinders ofsaid assemblies are disposed co-axially on opposed sides of saidinterlocking valve means and secured thereto and said pistons, when intheir starting positions, abut said sliding piston when the latter is inits neutral position.